1. Technical Field
This invention relates to power adapters, and more specifically, to a system, method, and apparatus housed within a power adapter tip to control a supply voltage for use by an electronic device coupled to the tip.
2. Description of the Related Arts
There are power systems in the art which provide an interface between a power adapter and an electronic device to regulate the amount of power supplied to the electronic device. Such power systems include the power adapter, a cable coupled to the power adapter, the electronic device, and a “tip” to interface between the cable and the electronic device. The cable or tip can include resistors which passively control the amount of voltage output by the power adapter.
There is a power system which has a power adapter which utilizes the following signals: (a) a programming voltage (Vprog), (b) ground (GND), and (c) an output voltage (Vout) to supply to the electronic device. Vout is produced by the power adapter and can be controlled by coupling a resistor of a set value between Vprog and GND. The Vout produced depends upon the resistor value. Accordingly, the resistor is used to “passively program” Vout.
Such a power system produces at the output of the power adapter the Vout determined by the resistor value. Vout from the power adapter is applied to a first end of a cable, the second end of which is coupled to the electronic device. The cable as an internal resistance. As a result of this internal resistance, there is a voltage drop across the cable. For example, if 1 Amp of current is supplied by the power adapter, and the cable has an internal resistance of 0.5 Ohms, there will be a 0.5 Volt voltage drop across the cable. Therefore, if the resistor sets Vout supplied by the power adapter at 12 volts, only 11.5 volts will actually be available to the electronic device. Alternatively, if 0.5 Amps of current is supplied, then the voltage drop would be 0.25 Volts ((0.5 Amp)×(0.5 Ohms)). The internal resistance of cables may be dependent upon the materials from which the cable is formed, the length of the cable, etc. Accordingly, even if Vout of the power adapter is passively programmed to be 12 Volts, for example, current systems do not ensure that 12 Volts are actually supplied to the electronic device, due to the internal resistance of the cable.
Also, systems which passively program the voltage are slow to compensate for fluctuations in the output voltage amount. For example, if the electronic device being powered is a DVD player, when the motor starts spinning, the DVD player will draw more current than had been drawn before its motor started spinning. Accordingly, the load will substantially increase, resulting in a lower Vout, which must then be corrected. Typically, the power adapter is a regulated power supply which includes a feedback path from its output to control the regulation. Thus, the power adapter will compensate for the decrease in Vout by supplying more current, thereby raising Vout (at the output of the power adapter) to the correct voltage level. The power adapter itself detects the change in the load and compensates for the increased load. Since the power adapter detects the load change at its output, rather than at the input to the electronic device (the cable being therebetween), there is a lag time between when the load changes and when the Vout is changed.
Current systems also do not protect the electronic device if the adapter operates improperly and supplies too much power to the electronic device. This excess power can result in damage to the electronic device. Moreover, a user has no way to quickly determine whether the adapter is malfunctioning.
Accordingly, prior systems would be improved if the actual amount of voltage supplied to the electronic device would be regulated at the input to the electronic device rather than at the output of the power adapter, eliminating the effect of the voltage drop across the cable. It is also desirable to decrease the response time (i.e., increase the loop gain) between when the load of the electronic device changes and when Vout is compensated to the correct level, as compared to current systems. It is further desirable to interrupt the supply of power to the electronic device if a malfunction of the system is detected and to provide the user with an indication of such malfunction.